There are in principle two different systems for conveying of workpieces by means of workpiece carriers. In one example system, the workpiece carriers are connected to a conveyor belt at fixed intervals. The conveyor belt is moved on in a clocked manner and thus travels the workpiece carriers from one position to the next. However, in this system the clocking has to be controlled based on the longest lasting process and that no channeling in or out of workpiece carriers can take place.
In another example system, the conveyor chain runs continuously and the workpiece carriers are taken along by the conveyor chain by means of frictional grip or the workpiece carriers are stopped by external stops and separators in front of processing points. The workpiece carriers can be diverted into secondary tracks via track switches and channeling-in and channeling-out devices.
However, in such systems the workpiece carriers may accumulate in certain situations in front of a processing point or transfer point. Due to such accumulations high strains may arise for the chain by the frictional forces acting on the chain and said high strains have to be taken into account in the design of the chain. In addition, considerable wear arises at the chain and at the entrainers of the tool carriers due to the constant friction. To minimize the wear, the chain is designed as large as necessary, in order to keep the friction force as small as possible. There are different approaches for this purpose, especially with heavy workpieces.
A workpiece conveying device for heavy workpieces having a plurality of workpiece carriers is known from EP 0 203 898. The workpiece carriers in this respect comprise a workpiece carrier for receiving the workpieces and a respective rotatable front and rear guide segment which establishes a connection with the belt arranged thereunder by means of a sliding shoe. The workpiece carriers are taken along by the belt by means of the friction force. The setting of the contact force for the sliding shoe takes place by selection of a suitable spring. Additionally or alternatively the preload force of the spring is correspondingly set by suitable underlaid disks. In this embodiment, the contact force is construed and set once and cannot be variably adapted to current demands.
In another example, DE 201 21 809 U1 describes a low-profile accumulating conveyor capable of negotiating curves and having a transport trolley. An adjustable entrainer is arranged at the lower side at the center of the transport trolley and it receives in its interior a friction element which is pressed down by a spring, which in turn is pressed against the surface of a pallet belt conveyor and which thus takes along the transport trolley. Contact force is applied by means of a compression spring which acts on the friction element. Its contact pressure is adjustable via a screw. The contact pressure is set such that the friction is respectively sufficient to move the transport trolley forward together with the supported load with the aid of the friction grip between the friction element and the pallet belt conveyor. The transport trolley itself in this respect rolls off on the transport belt with four individual casters.
However, in this embodiment, one potential issue is that every single entrainer of a transport trolley has to be set individually. Since there is no indication of the set force, this is a very time-consuming process. It must be checked individually by trials at each transport trolley whether the contact force is sufficient for the taking along. The user therefore tends to ensure in every case that the contact force is sufficient. There is therefore the risk in this respect that work is carried out with contact forces which are too high for safety reasons in order to ensure a reliable taking along in each case. However, this is then at the cost of the wear of the chain and of the workpiece carrier entrainer. If the accumulating conveyor is frequently converted and if different workpieces and thus transport trolleys of different weights are utilized, this requires a conversion process which may be time-consuming.
It is the object of the present disclosure to provide an adjustment mechanism for the contact force between entrainers and the belt with which a simple adaptation to different workpiece weights can take place in a simple manner for a plurality of workpiece carriers and with which a value which has once been set can be set reproducibly again—e.g. in the case of a workpiece change.
If this setting value has namely once been determined, it can also be stored for specific workpiece/workpiece carrier combinations or it can be noted on the workpiece carrier, and is available for the next conversion procedure as a predefined setting value. If the workpiece carriers and the chain have a certain wear after some time, the set values can be directly corrected without complex trials and adjustment work being required at each individual workpiece carrier.
This object is achieved by a workpiece conveying device for transportation of workpieces, comprising a conveyor chain for conveying workpiece carriers by transmitting friction forces; a U-shaped guide track for guiding and supporting the conveyor chain and the workpiece carriers; wherein support surfaces of the device extend next to the U-shaped guide track and the workpiece carriers are supported with guide rollers on said support surfaces, wherein each of the workpiece carriers are equipped with a front and a rear carriage which are provided with an adjustable entrainer for engagement into a U-shaped cut-out, wherein the adjustable entrainer for each of the workpiece carriers is designed via a foot part with an adjustable contact force to overcome sliding friction, and wherein the adjustable entrainer with a foot part has a display device for visualizing the set contact force.
In a further embodiment the object is achieved by a method for adjusting a plurality of workpiece carriers for a workpiece conveying device, comprising conveying the plurality of workpiece carriers on a conveyor chain by transmitting friction forces, wherein a U-shaped guide track guides and supports the conveyor chain and the workpiece carriers. The support surfaces extend next to the U-shaped guide track, the workpiece carriers are supported with guide rollers on the support surfaces; setting a contact force on an entrainer to overcome sliding friction, the entrainer provided on front and rear carriages of the workpiece carriers, and engaged into a U-shaped cut-out; visualizing the set contact force on the entrainer on a display device coupled to a foot part of the entrainer; setting the contact force on a first of the plurality of workpiece carriers by reading off a value from the display device; and transferring the set contact force to a remainder of the plurality of workpiece carriers.
Workpiece transport devices such as described in the present disclosure are transport devices in which the workpiece carriers are taken along by a transport chain by means of friction force. The transport chain in this respect frequently runs in a U-shaped cut-out at the center of a base belt body, driven by one or more electric motors. The workpiece carriers typically have two guide feet which stand on the chain in the U-shaped cut-out so that the transport chain can take along the workpiece carriers by means of friction force. Workpiece receivers are mounted on the workpiece carriers and are typically individually configured for the workpieces to be transported. In addition, the workpiece carriers are, just like the chain, guided laterally in the cut-out.
One or more workpiece carriers are accumulated in front of a processing station by a stop. Separator one of the guide feet of the frontmost workpiece carrier may be prevented from its forward movement by an inwardly pivotable abutment. In this respect, the belt runs continuously further beneath the tool carriers. If the stop or the separator is opened again, the transport chain again takes along the accumulated workpiece carriers until the stop or the separator is closed again.
Since the workpiece carriers lie loosely on the belt, they can, where necessary, be channeled out of the direct part flow by channeling in and out points and transported to separate processing stations. The workpiece carriers together with the workpieces arranged thereon can be raised by a separate lifting station at the processing station for the transfer of the workpieces to a processing device so that the workpiece can be raised from the workpiece receiver and can be processed. The workpiece can again be placed onto the workpiece receiver subsequent to the processing. Depending on the process sequence, the workpiece can, however, also be placed on an empty workpiece carrier arriving later.
With heavy workpieces, an attempt is made to configure the transport system for the workpieces such that substantial portions of the workpiece weight are taken up via additional rollers at the workpiece carriers. These rollers run on the base belt body or on special roller rails next to the base belt body.
Unlike with small workpieces in which the complete weight of the workpiece and workpiece carriers bears on the chain, there is the possibility with the embodiment in accordance with the present disclosure to design the transport belt/transport chain smaller due to the splitting of forces, for it only has to apply the force for overcoming the rolling friction which is necessary to move the workpiece carriers along the conveyor path on casters. In addition, the contact force which acts on the chain and which is necessary so that the workpiece carriers are taken along by the chain, may be adjustable.
There are different possibilities for applying this contact force to the belt in an adjustable manner. The simplest one is certainly that by means of a spring whose spring travel is variably adjustable by means of mechanical elements. In the embodiment in accordance with the present disclosure, the adjustment device is connected to a display device by means of which a characteristic value for the set spring force can be visualized. For example, it may be a display which maps the linear adjustment of the spring space, but may also be a pressure display which indicates the actual contact force. It is important that the display delivers reproducible characteristic values for the set contact force such that, the required force for taking along the workpiece carrier can be determined at a workpiece carrier. This is then transferred to the other workpiece carriers at the transport device by taking over the set and determined characteristic values.
If a specific wear is reached at the chain and at the entrainers after a specific time of use of the device, the contact force may be adjusted relatively easily in that the new setting value is determined at a workpiece carrier and said setting value can subsequently be transferred to the other workpiece carriers.
If different workpiece types are conveyed by one and the same transport device, the workpiece carriers can also be set to different contact forces. The user then also has the possibility by the visualization of the set values to check immediately whether the correct values are also set for the current workpiece type.
When necessary, this may take place, via an external control device, especially when the workpiece carriers are equipped with an individual marking or with a workpiece carrier identification device such as an RFID or a data carrier. An optical evaluation of the display or an electronic data transfer of the set values would be required for this. This would be of interest if the transport device runs over large paths within a factory automatization for linking a plurality of machines. A simple visualization is certainly sufficient for a simple machine automatization.
In a further embodiment of the present disclosure, the display device is protected from unintentional adjustment by a protective cover. It can thus be prevented that the contact force is adjusted in an unwanted manner on the handling of the workpiece carriers or of the workpieces on and with the carriers. The adjustment apparatus and its display device are furthermore protected against damage.
It would furthermore be possible to configure the protective cover such that it additionally prevents an unwanted adjustment of the contact force in that the cover achieves a blockage of the adjustment movement in a specific position. This could be achieved by a mechanical blockage apparatus which engages into or at one or more cut-outs or surfaces at the adjustment device. A clamping function would furthermore be possible which the protective device exerts on the adjustment device.
To adjust the adjustment device, the protective device can release the adjustment device by raising, tilting, displacing or rotating such that it can be adjusted. After the adjustment procedure, the adjustment device can be blocked again by a reverse movement.
Further features, details and advantages of the present disclosure will be explained in more detail in the following with reference to a plurality of drawings.